Notes Payable, Current Maturities and Debt: Schedule of Short-term Debt and Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Short-term Debt [Line Items]
Notes payable	$ 319,125		$ 349,500
Letters of Credit	17,281		30,274
Net (payments) borrowings of short-term debt	(30,375)	$ (20,970)
Commercial Paper
Short-term Debt [Line Items]
Notes payable	$ 154,125		349,500
Short-term interest rate	1.74%
Revolving Credit Facility
Short-term Debt [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 750,000
Notes payable	165,000		0
Letters of Credit	$ 17,281		$ 30,274
Short-term interest rate	1.92%